In a cellular communications system, the area over which service is provided is divided into a number of smaller areas called cells. Typically, each cell is served from a base transceiver station (BTS) which has a corresponding antenna or antennas for radio transmission to and reception from a user station thereby forming a radio communications link. The user station is often a mobile station. An established harmonised cellular radio communications system is the Global System for Mobile Communications (GSM). A further harmonised system currently being defined is the Universal Mobile Telecommunications System (UMTS), which is intended to provide a harmonised standard under which cellular radio communications networks and systems will provide enhanced levels of interfacing and compatibility with other types of communications systems. This will involve increased levels of data services including provision for multimedia communications.
Within systems such as UMTS or the like, user stations will increasingly be employed as general data terminals required to run or operate a plurality of processing applications simultaneously. Cellular communication user stations conventionally operate more than one processing application simultaneously, although these have tended to be relatively simple applications related to the basic functioning of the user station. Such simple applications share processing resources of the user station, the sharing of resources being conventionally managed by an operating system. It is expected that cellular communication user stations will increasingly resemble fixed local area network (LAN) data terminals, and that consequently the operating systems running on such user stations are expected to increasingly resemble operating systems for fixed LAN data terminals or computers.
However, a problem with the expected trend is that conventional data terminal operating systems for sharing processing resources between different applications running simultaneously are not fully satisfactory when applied to a cellular communications user station, especially a mobile station, as they do not make any accommodation of any special factors introduced by the need to share cellular communications resources, that become relevant due to the involvement of the radio link, between the different applications.